I'll reply to this, not really for a pc spec recommendation, but moreover, a recommendation for you, if you're looking to get into boxing, be prepared for a lot of hate, and ganking, particularly in the early levels. you will be camped mercilessly. a modern pc can handle much, I wouldn't be surprised if there are guys out there doing 30 on one pc. I have a eleven year old pc and can handle 13 with no issue. a simple google search can help.
I feel a lot of guys start this, and aren't prepared for the amount of hate you're in for, so I wanted to chirp in about that... if you aren't phased by it, or are prepared for it, welcome@ It is extremely fun.